42 THE REIGN OF LAW. 



controlling principle of construction, is so im- 

 pressed on Mr Darwin's mind, that, in every de- 

 tail of structure, however singular or obscure, he 

 has absolute faith that in this lies the ultimate 

 explanation. If an organ is largely developed, it 

 is because some special purpose is to be fulfilled. 

 If it is aborted or rudimentary, it is because that 

 purpose is no longer to be subserved. In the case 

 of another species whose structure is very singular, 

 Mr Darwin had great difficulty in discovering how 

 the mechanism was meant to work, so as to effect 

 the purpose. At last he made it out, and of the 

 clue which led to the discovery he says : — " The 

 strange position of the Labellum perched on the 

 summit of the column, ought to have shown me 

 that here was the place for experiment. I ought 

 to have scorned the notion that the Labellum was 

 thus placed for no good purpose. I neglected this 

 plain guide, and for a long time completely failed 

 to understand the flower." * 



When we come to the second part of Mr Dar- 

 win's work, viz., the Homology of the Orchids, we 

 find that the inquiry divides itself into two separate 



* p. 262. 



